I bought a wordpress theme for 25$. It is licanced under gpl v2. I read the licence, but my english is not that good enough to understand all of it. The question is, can I share this theme with my friends or random people on the web? I googled it and couldn't find a good answer to that. Please help me.

It might be good to actually link the theme, but I think that you can redistribute GPLv2 work to anyone you want as long as you don't restrict it further. The fact that you paid for a copy doesn't change that.

Yep you can certainly sell GPLed works as long as you follow the provisions of the license, for instance you must allow others the same freedoms. For something that contains graphic art or sound you should check the license of those parts, the restrictions on those may be different. For example, the Quake game engine code are GPL, but the models, textures and sound elements cannot be redistributed without permission.